It has been known that urethane (meth)acrylate compounds, epoxy (meth)acrylate oligomers and polyester (meth)acrylate oligomers are oligomers which undergo curing by active energy rays such as ultraviolet rays.
Urethane (meth)acrylate compounds, when cured, form tough, high-mechanical-strength polymers which also exhibit high chemical resistance. Their cured polymers have excellent adhesion with a variety of materials and satisfactory processability. Urethane (meth)acrylate compounds are therefore widely employed as bases in different types of active energy ray-curing inks, paint coating compositions and adhesives.
Particularly, in the field of manufacturing printed wiring board, in resists and solder resists, more specifically in solder resists employed in manufacturing processes for film-like printed wiring boards (flexible printed circuits, or FPCS) for miniature devices, photosensitive compositions comprising urethane (meth)acrylate compounds as major components are being widely utilized. That is, in methods wherein a photosensitive composition is printed to form a cover coat on, or is attached as a film onto, a substrate, the coating of the photosensitive composition formed on the substrate may be followed by exposure, development, and heating to allow easy formation of intricately patterned cover coats or coverlays. Use of such photosensitive compositions offers advantages over conventional polyimide films as no expensive molds are necessary, the effort and cost of the attachment operation are not required, and intricate patterns can be easily formed.
Such photosensitive compositions must exhibit different properties depending on the intended applications. The important properties for use in electronic parts include heat resistance, insulation properties and flexibility, as well as flame retardance, since the applications are limited if the flame retardance is low.
With conventional photosensitive compositions, however, it has been difficult to provide satisfactorily high flame retardance. Methods of the prior art for imparting flame retardance include those using flame-retardant systems comprising halogenated flame retardants such as brominated epoxy resins, or combinations of these with flame retardant aids such as antimony trioxide (Japanese Unexamined Patent Publication HEI No. 9-325490, Japanese Unexamined Patent Publication HEI No. 11-242331). However, these flame-retardant systems have often been poorly reliable in high-temperature environments. Brominated epoxy resins have been associated with the problem of impairing flexibility when they are added in amounts sufficient to produce an adequate flame-retardant effect.
In recent years, restrictions have begun to be placed on halogenated resins such as decabromo ethers, in light of the problem of dioxins. Dehalogenation and elimination of antimony are also becoming requirements for resin molding materials used in electronic parts. This has also imposed a limit on the degree of improvement in flame-retardant effect achieved by addition of conventional types of flame-retardants.
Methods of using phosphoric acid esters as flame-retardants have been proposed (Japanese Unexamined Patent Publication HEI No. 9-235449, Japanese Unexamined Patent Publication HEI No. 10-306201, Japanese Unexamined Patent Publication HEI No. 11-271967, and others), but a simple inclusion of phosphoric acid esters in a composition gives a weak flame-retardant effect and fails to adequately meet the UL standards established for flame retardance.
A demand therefore exists for development of photosensitive compositions with high flame retardance while achieving dehalogenation and elimination of antimony.
It is an object of the present invention to provide urethane (meth)acrylate compounds with high flame retardance, as well as photosensitive compositions with excellent flame retardance in addition to such properties as photosensitivity, development capability and flexibility.